Shiga Toxin: A Public Health Threat

Norman Moore, PhD Director of Scientific Affairs, Infectious Diseases, Alere

Objectives

Discuss the clinical significance of Shiga-toxin producing E. coli (STEC) and its effect on public health Demonstrate how STEC can be transmitted and what foods are at

highest risk Review the ways in which STEC causes significant illness, especially in

younger children Analyze the need for and how to test and treat for STEC

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Top 7 Threats to the Human Race

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Source adapted from Science, Vol 325, September 2009 Available at http://www.sciencemag.org/content/325/5948.cover-expansion

Infectious Disease & Antibiotics

1970: Surgeon General William Stewart said the US was “ready to close the book on infectious disease as a major health threat” • Modern antibiotics, vaccination, and sanitation methods had done

the job

1995: Infectious disease is the 3rd leading cause of death behind heart disease & cancer

Infectious disease remains a critical concern as antimicrobial resistance increases

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Antibiotic Overuse

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One in every three inpatients will receive 2 or more antibiotics in the course of their hospital stay

Of the inpatients receiving antibiotics, 3/4 will receive unnecessary or redundant therapy

Each year, tens of millions of antibiotics are prescribed unnecessarily for viral upper respiratory infections

CDC – Get Smart Campaign

Costs of Antibiotic Resistance

Antibiotic resistance increases the economic burden on the entire US healthcare system • Resistant infections cost more to treat and can prolong healthcare

use

More than $1.1 billion is spent annually on unnecessary antibiotic prescriptions for respiratory infections in adults

In total, antibiotic resistance is responsible for:

• $20 billion in excess healthcare costs • $35 billion in societal costs • 8 million additional hospital days

6 CDC – Get Smart Campaign

“A post-antibiotic era means, in effect, an end to modern medicine as we know it.

Things as common as strep throat or a child’s scratched knee could once

again kill.”

Margaret Chan, WHO Director General

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Why Antimicrobial Stewardship?

A balance of infection prevention and antibiotic management Achieve optimal clinical outcomes Decrease adverse drug events

• C. difficile

Minimize development of antimicrobial resistance Preserve antimicrobial resources Reduce costs

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Antimicrobial Stewardship Programs

Guidelines for Developing an Institutional Program to Enhance Antimicrobial Stewardship – 2006

http://www.idsociety.org

Core members include: – Infectious Disease Physician – Clinical Pharmacist – Clinical Microbiologist – Infection Control Professional – Information System Specialist

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Rapid Diagnostics

Test, Target, Treat

• Know the organism, know the appropriate treatment

Reduce antibiotic overuse & unwanted side effects

Shorten time to appropriate therapy

Provide targeted treatment with narrow-spectrum agents when possible

Reduced infection transmission increases infection prevention savings

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Gastrointestinal Disease: Impossible but True

Impossible to diagnose on clinical symptoms alone, but frequently done What’s the primary symptom of any GI disease?

100s of causes, often treated empirically with antibiotics

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Diarrhea in the World

Worldwide, it kills 1.5 to 2.5 million children per year • Second biggest killer of children

• More than HIV, TB, and measles combined • 5 to 18 cases/year

What can be done?

• Flush toilets, sewers, and waste water treatment • 19th century England – largest drop in child mortality ever • Flush toilet named best medical advancement in last 200

years

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What Can Travel in One Gram Feces?

1,000 parasite cysts

1 million bacteria

100 worm eggs

10 million viruses 13

Diarrhea in the US

211-375 million diarrheal illnesses/year • 21-37 million episodes in children under five • Adults average 1 acute case/year • Young children average 2 acute cases/year

73 million physician consultations

1.8 million hospitalizations

3100 deaths

$25 billion in healthcare costs

Foodborne Illness in the US

76 million illnesses

325,000 hospitalizations

5000 deaths

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IDSA Guidelines 2001

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Etiological Agents of Diarrhea

• Rotavirus, Norovirus, Cytomegalovirus (in immune compromised), Astrovirus, Adenovirus, etc.

Viral infections

• Campylobacter, Salmonella, Shigella, and E. coli

Bacterial infections

• Giardia lamblia, Entamoeba histolytica, and Cryptosporidium Parasites

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Escherichia coli (E. coli) Basic Information

Ubiquitous in the gut of healthy individuals & many animals • Most strains are not only harmless, but beneficial

May cause illness • Diarrhea • Urinary tract infections • Respiratory illness & pneumonia

Can be used to monitor water quality • Fecal coliforms are bacteria that live in stool of warm-blooded animals • Can have direct contamination of water with stool • Can have run-off from farm irrigation • Can have breaks in septic systems

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What are Shiga-Toxin Producing E. coli?

E. coli that can produce Shiga toxin (STEC) • Also called Entererohermorrhagic E. coli (EHEC) and

verocytotoxic E. coli (VTEC) • Identical toxin to what is produced in Shigella

Most famous is E. coli O157:H7 • Other non-O157 STEC serogroups that often cause illness in

people in the United States include O26, O111, and O103.

Shiga toxin • Comes in two main groups; Stx1 and Stx2 • Toxin that inhibits protein synthesis in target cells • Stx2 more associated with complications like HUS

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Additional Issues with STEC

Bacteria are often acid tolerant

Low infectious dose (<100 organisms)

More common during the

summer months

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What are the Symptoms of STEC?

• Many can be subclinical Varies per

person

• Diarrhea (potentially bloody) • Severe stomach cramps • Vomiting • May have fever

Main symptoms

• Usually 5 to 7 days Disease

Resolution 21

Complications of STEC

Of those diagnosed with STEC, around 5-10% can get hemolytic uremic syndrome (HUS)

Symptoms of HUS

• Bloody diarrhea • Decreased urination • Tired • Loss of pink color in cheeks and inside of lower eyelid

Major Issue of HUS

• Kidneys may stop working among other complications • People with HUS may recover in weeks, suffer permanent damage, or

potentially death

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How Do Patients Develop HUS?

Mechanism • The toxin causes the blood cells to

become misshapen • Blood cells can clog the tiny vesicles in

the kidneys known as glomeruli • Filtration by the kidneys becomes blocked • Kidneys may shut down

Usually children 23

Thrombotic Thrombocytopenic Purpura (TTP)

Mechanism • Toxin changes shape of the blood cells • Clots form in blood vessels • Oxygen does not get to organs like brain,

heart, and kidneys • Platelets get used up • Bleeding problems arise whether internally,

under skin, or cut

More likely in adults 24

Incubation Period

Average time between consumption of STEC to disease is 3-4 days • Time can vary from 1 to 10 days

Symptoms increase over time

• Stomach ache to mild diarrhea • Increases to more significant diarrhea to bloody diarrhea

HUS, if it happens, usually is around a week after initial symptoms

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STEC Stats

CDC estimates 265,000 cases per year in the US • E. coli O157:H7 accounts for roughly 36% of these

infections

Why aren’t they seen in hospitals?

• Many patients don’t seek medical attention • Those patients that do may not give a stool

sample • Laboratories may not be able to test stool samples

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Infecting Others

Typically, toxin-producing bacteria go away with symptoms

For some individuals, symptoms may resolve, but can still have STEC for months

Therefore, important to keep up appropriate handwashing!

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Transmission of STEC

• Directly from people not washing hands and touching others

• Indirectly from people not washing hands and handling food

• Daycares with diapers

Fecal oral route

• Meat can be directly contaminated during processing • Other foods like water runoff from cow pasture to farm Food exposure

• Lake/pool/water park • Petting zoos & other animal exhibits

Environmental Exposure

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STEC Transmission Community acquired Food & water borne Outbreaks

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Printed with permission from Ellin Doyle. From: Human Illness Caused by E. coli O157:H7 from Food and Non-food Sources. http://fri.wisc.edu/docs/pdf/FRIBrief_EcoliO157H7humanillness.pdf

Multistate E. coli O157:H7 in Ground Beef – June 2014

• 12 cases with 7 being hospitalized • Spanning 4 states • Zero deaths

Major statistics

• Contaminated ground beef at Wolverine Packing company

• 1.8 million pounds distributed to restaurants and retail throughout the nation

Why

• Recall happened AFTER use-by date • Consumers should check their frozen meat Action

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Multistate E. coli O121 in Raw Clover Sprouts – August 2014

• 19 cases with 44% hospitalization • 6 states • Zero deaths

Major Statistics

• Evergreen Fresh Sprouts, LLC of Idaho had contaminated raw clover sprouts

• In interviews, 81% of people ate raw clover sprouts the week before, often from local restaurants

Why?

• FDA inspection saw multiple unsanitary conditions often involving corroded metal in contact with food

• The suspect seed lot was discontinued Action

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Multistate E. coli O121 in Farm Rich Brand Frozen Food – May 2013

• 35 cases with 9 hospitalizations • 19 states • Zero deaths, but 82% were under 21 and 2

developed HUS

Major Statistics

• O121 found in frozen mini pizza slices Why?

• Recall expanded to include all Farm Rich, Market Day, and Schwan’s brand frozen food products Action

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Diagnostic Recommendations

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Why Should People Test?

Hydration • May want to treat with parenteral

volume expansion if it is early in the infection

Do not take antibiotics • Increases risk of HUS • Antidiarrheal agents like Imodium may

also increase risk of HUS 36

Antibiotics and STEC

Potentially fatal renal failure More prevalent in pediatrics Antibiotics may increase risk of HUS due to toxin

release from dying STEC cells

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Who should be tested?

CDC & Joint Commission: All acute community acquired diarrheas

Antibiotic use is common for GI disease, may be

deadly in a STEC patient Rapid identification of potential outbreaks

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Screening Criteria

Test if Risk

Visible blood Present Not all STEC positives have visible blood

Season Summer-Fall Can occur year-round, esp. with imported produce

Patient Age Pediatrics, Elderly

Not all cases are peds & elderly

O157 and non-O157 strains

O157:H7 is the most common US strain • Traditionally labs only tested for O157

Over 100 non-O157 strains cause disease • April 2013 outbreak of O121 • 2011 German outbreak of O104

• Over 3,500 cases, 23% developed HUS

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Detecting O157 vs. non-O157

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O157-specific Assays Assays for Toxins Test for O157 strain only Test for toxins Stx1 & Stx2 Will miss all non-O157 STEC strains

Will detect all toxin-producing strains

Plate culture (SMAC, mac-sorb) most common

Rapid assay or ELISA most common (may require broth enrichment)

CDC Recommendations

Test all stools from community-acquired diarrhea for STEC

Concurrent testing

• Culture stool for O157 • Testing for Shiga toxin

Actions

• All O157 STEC isolates should be forwarded to appropriate public health lab for confirmatory testing & additional characterization

• Results should be reported promptly to physician

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Rationale for CDC Recommendation

There are publications supporting that STEC may be as common as other bacterial pathogens • STEC (0% - 4.1%) • Salmonella (1.9% - 4.8%) • Campylobacter (0.9% - 9.3%)

Early diagnosis is important for proper treatment

• Volume expansion for O157 • No antibiotics to lessen risk of HUS

Help detect outbreaks earlier

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Why Every CA Stool?

Many infections can be missed when having selective strategies • Just children • Just summer

Some STEC don’t have visible blood and other pathogens may

Pathogens will be more difficult to recover from stools at a later date

Help prevent transmission to others

• Children may not be able to return to daycare facilities • Food service workers

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E. coli O157 Culture

Plate on sorbitol-MacConkey agar plate or chromogenic agar • O157 does not ferment sorbitol within 24 hours

Wait 16-24 hours @ 37°C

Look for color • SMAC plates have colorless colonies • Chromogenic agar has specific colony colors

Test well-isolated colony on antiserum or latex • Screen at least 3 colonies

Preliminary findings reported

Confirmatory testing

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Shiga Toxin Assays

Major benefit • Detects all Shiga-toxin producing E. coli rather than just O157

What to test? • See manufacturer’s product inserts on what is approved

Direct stool • Fresh • Frozen

Cultures • Broth culture • Plate culture

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Stool testing For Shiga Toxin

Major Benefit – Detects toxin producers beyond E. coli O157

Direct stool detection provides real-time actionable results

• Initiate proper treatment while patient is in the healthcare setting • Avoid antibiotic exposure

Ideal for emergency situations, pediatrics with bloody diarrhea

Identify potential outbreaks sooner

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Molecular Assays

No single Shiga-toxin assay available, but have multiplex assays

Public health laboratories may use home brew molecular

Can be done on isolated colonies or clinical samples

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How Does Broth Culture Compare?

2 published studies from Alberta, Canada looked at performance of rapid assays vs. in-house PCR • “EHEC Assay” study compared market leader in 2013 to PCR • “STEC Assay” wasn’t available then, study done in 2014 • Similar regional demographics, methods, similar sample size,

prevalence rate

Both assays used broth enrichment culture

STEC Assay also tested directly on stool specimens

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Chui L, et al. Diag Micro Infect Dis 2013. 77(2013): 8-13. Chui L, et al. J Clin Micro e-pub 14 Jan 2015

Broth Culture Comparison

EHEC Assay not recommended as a routine screening test for STEC from broth cultures due to low sensitivity and risk of false positives

STEC Assay is a viable alternative to molecular testing for frontline labs as a primary screening method for STEC.

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n = 819 Sensitivity PPV EHEC Assay (broth culture)

35% 54.5%

n = 784 Sensitivity PPV STEC Assay (broth culture)

85% 100%

Broth Culture Comparison

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n = 819 Sensitivity PPV EHEC Assay (broth culture) 35% 54.5%

n = 784 Sensitivity PPV STEC Assay (broth culture) 85% 100%

Majority of true positives not detected

More positives detected

Almost half of all positive results were false positive

All positive results were confirmed as true positive

PPV = Positive Predictive Value

Preventing STEC

Hand washing! • After restroom • Changing diapers • Prior to preparing food • Contact with animals

Prepare food appropriately • Make sure meat – especially ground beef – is cooked thoroughly • Don’t use cutting board for meat and then other food • Clean cutting boards

Avoid drinks that are unpasturized that are supposed to be • Raw milk • Dairy products • Apple cider

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Discussion

Shiga toxin producing E. coli are a significant health risk

Diagnostic testing can help better direct therapy

Appropriate therapy can reduce complications, such as HUS and TTP

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